The general concept of boring is to offset a cutting edge from a driven axis of rotation to make a cut having a radius of the offset.
FIG. 1 is a front elevation view of a conventional prior art adjustable boring head 70 further showing in phantom a conventional prior art boring tool, such as boring bar 100 mounted therein. FIG. 2 is a left side view of the prior art boring head 70 of FIG. 1 further showing in phantom a drive shaft 120. FIG. 3 is a bottom, front, left side perspective view of the prior art boring head 70 of FIG. 1.
Boring head 70 has a front 68 and a back 69 and generally includes a body 71, a boring tool holder, such as boring bar holder 80, and radius adjustment means, such as dial screw 90, for adjusting the radius of the cut. The top 78 of body 71 includes mounting means, such as threaded bore 72, shown in phantom, having an axis 79, for attachment of a drive 120, shown in phantom. A typical drive 120 is a shank having a lower end adapted, such as by being threaded, for attachment to bore 72, and an upper end, not shown, adapted for attachment to the drive spindle of a machine, such a milling machine. Typically, the upper end is tapered for mating to a drive spindle or is straight for mating with a collet that is tapered for mating with the spindle. Drive 120 is a cylindrical shaft, typically of three-quarters inch or seven-eighths inch diameter or greater. Typically, drive 120 is three quarters inch diameter for a two inch diameter boring head.
Body 71 includes a left side bore 74 for travel of head portion 94 of dial screw 90, a horizontal threaded bore 73 for receiving screw portion 92 of dial screw 90, and a fully transverse dove tail slot 75 in the bottom of body 71.
Bar holder 80 has a front side 81 and a top including a dove tail 82 slidingly mounted in dove tail slot 75 of body. Bar holder 80 includes three holes, such as cross bore 83 and vertical bores 85, such as medial bore 85A and lateral bore 85B. Each bore 83, 85A, 85B is adapted for holding a tool, such as a boring bar 100 Cross-bore 83 is a horizontal bore, shown in phantom in FIG. 1. Means, such as set screw 84 in a threaded bore, is provided for retaining a boring bar 100 in cross hole 83. Medial bore 85A is located near the middle of bar holder 80 for receiving a tool, such as a boring bar 100. A set screw 86, such as set screw 86A, in a threaded bore, retains boring bar 100 in medial bore 85A. Lateral bore 85B is located in bar holder 80 laterally of medial bore 85A for receiving a tool, such as boring bar 100. A set screw 86, such as set screw 86B, in a threaded bore, retains boring bar 100 in lateral bore 85B. Medial bore 85A has a longitudinal axis 87A and lateral bore 85B has a lateral axis 87B parallel to axis 87A. Vertical bores 85 are generally about three-eighths inch to one-half inch diameter, such that the diameter of an inserted boring bar 100 is much less than the diameter of drive 120.
Boring bar 100, shown, is an elongate generally cylindrical shaft, such as of high speed steel, with its cylindrical shank 102 mounted in lateral bore 85B. Boring tool 100 includes a lower end including a location 104 adapted for having a cutting edge 105. Cutting edge 105 may be integral with bar 100, such as if the bar is of high speed steel, or may be on an attached insert 106, as shown in FIGS. 4 and 9 of the current invention.
Dial screw 90 adjusts the radius of cut of cutting edge 104 by moving bar holder 80 horizontally relative to body 71. Dial screw 90 includes a machine screw portion 92 in threaded bore 73 in body 71 and a head portion 94 attached thereto including an annular groove 95 and a graduated dial 97. Rotation of dial 97 moves screw portion 92 in threaded bore 73 and moves dial screw 90 horizontally. A tooth or web 89 on top of bar holder 80 engages annular groove 95 in head portion 94 of dial screw 90 so as to move bar holder 80 horizontally with dial screw 90. Gib screws 76 in bores in body 71 bear against dove tail 82 to adjust play in the dove tail joint and include a set screw 77 for locking dove tail 82 and hence bar holder 80 at a selected dialed position.
With boring bar 100 mounted in medial bore 85A, dial screw 90 can be adjusted to bore a first range of radii. With boring bar 100 mounted in lateral bore 85B, dial screw 90 can be adjusted to bore a second range of radii; the second range generally overlapping the first range.
There are several drawbacks to mounting a conventional boring bar 100 in boring head 70. One drawback is that a boring tool, such as boring bar 100, is attached thereto with just a set screw, such as set screw 86, that is typically tightened on a round mounting shank, such as shank 102. Because cutting edge 105 is offset on the shank, a rotational force is produced that set screw 86 sometimes cannot resist. Consequently, shank 102 sometimes slips on set screw 86 and rotates in bore 85, which is undesirable.
Another drawback of mounting a conventional boring bar 100 in boring head 70 is that that the diameters, and hence the strengths, of conventional boring tools 100 that can be mounted are much smaller than the diameter and strength of drive shaft 120. The lower strength boring bar 100 may break, deflect, vibrate or chatter; any of which is undesirable.
Therefore, it would be desirable to have an improved boring tool for mounting in a boring head of the type shown and described wherein the improved head is not subject to rotating in the mounting bore and is not as subject to breaking, bending or chattering.